Loud-speaker with diaphragm an integral part of outer casing



F. MAssA 6, LOUDSPEAKER WITH DIAPHRAGM AN INTEGRAL PART OF OUTER CASING Filed July 25, 1945 Patented Feb. 7, 1950 UNITED LOUD-SPEAKER WITH DIAPHRAGM AN INTEGRAL PART OF OUTER CASING Frank Massa, Cleveland Heights, Ohio Application July 23, 1945, Serial No.-606,'557

Claims.

My invention is concerned with electro-acoustic transducers, and, more particularly, with transducers whose vibrating systems are stiffnesscontrolled over a large portion of the frequency range of operation.

In a vibrating system that is stiffness-controlled, the mechanical stiffness of the vibrating element offers practically all the impedance to the alternating force which is used to set the system into vibration. Stiiiness-controlled vibrating systems are well-known in the art. A very common transducer employing a stiffness-controlled vibrating system is the conventional telephone receiver in which a magnetic disc is clamped near its periphery and is driven by magnetic forces generated within the unit. In the frequency region over which the diaphragm stiffness is the controlling impedance, the displacement of the diaphragm per unit driving force is independent of frequency, which results in approximately constant sound pressure in the ear provided the receiver is properly sealed thereto. In the telephone receiver, the diaphragm, which is relatively flexible, is enclosed by a cover.

It is a purpose of my invention to provide a transducer in which the mechanical stiffness of the vibrating diaphragm is very much higher than the stiffness employed in the conventional type of telephone receiver so that the diaphragm may be designed as one of the external surfaces of the transducer and yet remain ruggedeven under rough conditions of handling.

The general procedure that I employ for constructing my new type of transducer is to mold two portions; a body portion including the pole pieces and magnet assembly as inserts in the molded part, and a diaphragm portion including a magnetic armature assembly molded as an insert. The diaphragm portion consists of a relatively thick convex shell which is somewhat thinner in the region defining the vibratile section of the piece. These two inexpensive halves are then made flat over their mating surfaces and are bonded together to form a very simple hermetically sealed unit. To secure maximum strength for the transducer, the external surface is designed to approximate a smooth, flattened ellipsold.

In one application of my new transducer, it is placed under a pillow and is connected to a radio to reproduce a program directly to a person lying in bed. For this use, the weight of the persons head which is transmitted through the pillow to the vibratile section of the diaphragm portion of the structure, must notdeflectthe diapragm to an with an input of about one volt applied to the transducer terminals. The impedance of the transducer measured approximately 200 ohms at 1000 cycles. ducer was about 3 /2 inches and the diameter of the under-cut vibratile section of the diaphragm portion was approximately 2 inches. When this transducer was held in the hand, it felt about the same as a solid Bakelite object and there was no sense of flexibility to the diaphragm surface as would'be the case if a conventional telephone receiver were held with its diaphragm surface exposed to the touch.

In a somewhat smaller version of my new transducer, designed for use as a portable microphone which is impervious to weather conditions or which may be covered with a very soft smoothsurfaced cushion for use as a comfortable head set, I find that a diaphragm compliance as high as .601 inch deflection per pound of force applied to its center point is possible without sacrificing the desirable ruggedness and reliability features of my simplified transducer.

A better understanding of my invention will become apparent after reading the specifications and claims which follow:

An object of my invention is to improve the ruggedness of an electro-acoustic transducer of the vibrating diaphragm type.

Another object of my invention is to simplify the construction of a transducer, thereby resulting in lowering its manufacturing cost.

A further object of my invention is to provide a transducer in which the vibrating diaphragm is an integral part of the external surface of the structure and having sufficient rigidity so that the performance is not materially affected by resting the weight of a persons head over the surface of the diaphragm.

Another object of my invention is to mold the magneticmaterial of a magnetic type of transducer as inserts into the major portions of the structure, thus eliminating the cost of mounting the magnetic structure separately.

A further object of my invention is to provide a transducer design in which two portions are scaled together thus totally enclosing the force Theoverall diameter of this transgenerating mechanism and eliminating the need for screws or other fastening devices.

A still further object of my invention is to provide an enclosed housing of which one surface is designed to act as a vibratile diaphragm and within which enclosure is mounted the electromechanical transducer mechanism which is operatively connected to drive the diaphragm surface.

Another object of my invention is to provide a method of manufacturing a transducer in which high mechanical precision results at a very low cost.

Still another object of my invention is to provide a simple anchor for a flexible cable sealed through the transducer housing so that the cable may be neither pulled out nor pushed into the housing.

A further object of my invention is to provide a transducer design which is completely waterproof.

Another object of my invention is to improve the design of a transducer so that improved comfort will result when the unit is worn as a head phone.

Other objects and advantages of my invention will become evident by reading the specifications which follow. The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention, itself, however, both as to its organization and method of operation, as well as advantages thereof, will best be understood from the following description of several embodiments thereof, when read in connection with the accompanying drawings, in which- Fig. 1 is a plan view of an electro-magnetic type of transducer which embodies the teachings of my invention. The diaphragm portion has been partially cut away to show the cable anchoring and other internal structural details.

Fig. 2 is a section taken along the line 2-2 of Fig. 1.

Fig. 3 is a section showing another magnetic type of transducer in which the polarizing flux is supplied from an electromagnet in the electrical circuit of the device.

Fig. 4 shows a cross-section of another type of transducer which embodies the teachings of my invention and makes use of a magnetostriction element as the transducer means.

Fig. 5 is a section through a transducer employing the teachings of my invention and employing a piezo-electric crystal as the transducer element.

Fig. 6 shows means for adapting one of my new transducer units so that it may be Worn as a head phone with improved comfort as compared with previous types of head phone constructions.

Fig. '7 is a section taken along the line 1-! in Fig. 6 showing the pivot means employed for allowing the head phone unit to adjust itself to a balanced position on the ear.

Referring more particularly to Fig. l and to Fig. 2 which is a section along the line 22 of Fig, 1, the reference character 1 represents the main body of the transducer which is preferably molded to the desired shape. During the molding of the body 1, two pole piece assemblies 2, together with a permanent magnet 3, are placed in the mold as inserts such that the lower portions of the pole pieces 2 and the entire magnet 3 are permanently embedded Within the material when the piece is made as indicated in Fig.

2. I have found it preferable to build up the pole piece assemblies 2 by cementing the necessary number of laminations in a fixture to produce the required thickness of the stack. The magnet 3 is also cemented to the pole pieces 2 so that the resulting sub-assembly is easily handled and used effectively as a solid single insert which is dropped into the mold during manufacture of the body I. As a result of this method of fabrication, an inexpensive magnetic transducer construction is realized in which all fastening devices to hold the critical magnetic components are eliminated and a clean, rugged unit is produced in which the magnetic materials are permanently imbedded within the structure with uniform accuracy.

Still referring to Figs. 1 and 2, the reference character 4 indicates the diaphragm portion of the transducer. A stack of armature laminations 5 are pro-assembled as previously described in connection with the pole piece 2 and the armature assembly 5 is then used as an insert when molding the diaphragm 4. The design of the diaphragm 4 has as one of its main objectives the possibility of allowing the vibrating surface to remain as an unprotected part of the complete external transducer surface, thereby producing a smooth, solid unit having the approximate external appearance of a flattened ellipsoid and not requiring any protecting grilles or other precautionary measures for preventing damage to the structure. In order to achieve this objective, I found it necessary to make the mechanical compliance of the diaphragm low enough so that a force of several pounds applied directly to the diaphragm surface will cause only a few thousandths of an inch displacement of its center point. For a transducer of this type, which I built for reproducing radio programs through a pillow when a person is lying in bed or reclining on a chair, I found it desirable to make the compliance of the diaphragm such that a force of five pounds applied to its center point would not cause more than .002 inch displacement. To achieve this order of magnitude of compliance, I found that a plastic diaphragm designed as shown by reference character 6 in Fig. 2, having an unsupported diameter of about 2 /2 inches and a material thickness at the thinnest portion of about resulted in a very practical structure of pleasing proportions and simple to produce. In another transducer of the same type designed primarily for use as a microphone and as a head phone and requiring an unsupported diaphragm diameter of about 1 /2 inches, I found that the diaphragm compliance could be as high as .001 inch displacement per pound of force applied to its center point. If the compliance were made appreciably higher, the ruggedness of the transducer would be impaired and it would become necessary to employ precautionary measures as is the general practice in head phones of conventional design in which the diaphragm is never exposed as an external surface of the structure, but is covered by a grille or the like.

Still referring to Figs. 1 and 2, two coils of wire 6 are placed over the exposed tips of the pole pieces 2 and are cemented to the flat internal surface of the housing I. The coil leads I are connected to terminal pins 8 which are forced into a pair of holes suitably located in the body of the housing I, which is molded of a non-conducting material. The fiexible cable 9 has a molded tapered sleeve I0 whose largest end is .also .introduce another that will causeincreased production variations f rcedint rthe entrancexholepinothe zbody l to aprovide :a snug, "moisturee'proof :fit between the 1 neither a pulled out -;nor,; pushed into the housing.

The-rcable leads are soldered to the pins es- ;tablishing electrical connection to 1 the .coils is.

siBefore "connecting the .two housing portions ltogether, ,the diaphragm portion '4, with its .molded insertarmature assemblyt, is machined tolinsure that the exposedsuriace of the omma lture :5 {lies in the same plane as the mounting ziiacerof the aflange portionof the diaphragm 1 i. Thc'housing or back gportionil, with :itsimolded .insert pole piece assemblies :2, is i also. machined :so zthatrtheplane of the. pole tipslies paral-lelto -the plane-of the peripheral mounting face of the -=-housing sand :the plane of the .pole tip surfaces is set below the plane of the peripheral-mound .ing .facepf thelhousing-bythe distance required .for. establishing-the desired air g-ap at finaLas #sembly. In thefinalassembly ofthe diaphragm .portionsltothe backportion l, a film of. cement [1.3 employed between :the two surfaces that are shown in contact. Thehousing pieces-Lt and l .arepreferably .held. ina fixture whichinaintainsconcentricity .of the two parts and simul- .taneouslyzapplies a pressure to .insure intimacy .ofthe two surfaces beingbonded. By following #the described procedure, a completely enclosed, water-proof, rugged transducer results which permits uniformity of dimensional tolerances at .a .veryfllow cost of manufacture. lIt.is,.of course, obvious .thatscrews or other well-known means maylbe employed .for attaching .the diaphragm +4 .to thebody i; .howevensuch .an assembly will ;entail.-.an increase in manufacturing cost :and ,willnotresultiina bonded watereproof surface between the .two pieces unless a gasket .is employed, which will further increase the costand dimensional tolerance 'in the air 'gap dimensions.

In Fig. v3 is shown a cross-sectional view of another type 'of transducer employing the same basic structural design as has been described in "connection with "Fig. l. and 'Fig. ,flTheonly dif- Terence in this modified transducer is that the pole piece and magnet assembly of Fig. Z'has been replaced byastack of u-shapcd laminations 'l l which are molded as'an integral part of the hous ing I by'the method previously described. For thestructureo'f Fig. 3, a DJC.polarizing "current sentthrough the coils "d to establish the de- *magntos'triction element 15, as described in my co-pending application Serial No. 588,691, filed B April116,.19.l5, now U. STPatent No. 2,475,148, employed as the transducer means. A'special coil form it provides a suitable mounting-for. itself and also provides a locating surface for causing the bi-metallic strip [5 to'pass accurately'through' theiaaial openingv of the coil'form, the screw l lfbeing' used to secure the bi-metallic strip .l 5' to the coil form. A more complete description oithis constructional detail may he found in my co-pending application, Serial No. 598,270,:filed June 8, 1 9%. A coil of wire 18 is wound on the coil form is and the ends of the coil are suitably connected to a cable in a nianner similar to that shown in Fig. l. To the free end of the'bi-metallic niagnetostriction reed is attached the drive pin ill, which'is so located that it is aligned along the'central axis of the body l at assembly. The diaphragm portion a has a hole through its center which is countersunk at its outer edge, as indicated. After the diaphragm d and body lare assembled. as previously described, a hard cement 253 is used. toifill the small conical cavity exposed on the centeroi the diaphragm, thus securing an ii'itiniatg bond between the drive pin 19 and the diaphragm and also effectively sealing the trap ucer to makethe unit Water-proof.

11 g. 5 is shown another modification ofmy improved transducer in which a piezo-electric nt is employed as the transducer means. For this modification, the housing 5 has no molded inserts and a piece-electric crystal element such as a W11-lili10Wll Rochelle salt twister 2|, is at ..ched to the inside housing surface by :means oi mounting pads Themounting pads 22 are employed to mount three corners of the square crystal element on the fourth iree'corner is 'ured the drive pin ill which is so located that when the crystal is assembled, the pin I9 lies along the center axis of the housing. The diaphragm i is prepared identically as described in connection with s and the assembly also lollov-ms the identical procedure there described.

in 6 is shown the application'of my new type of transducer as an improvedform'of;head

the rivets 23. amat'se ial having the consistency of foamrubber phone. As previously mentioned, I finditprefenable-to lteep'the compliance of the diaphragm no higher than .001 inch deflection per pound of force applied at its center in order to insure ruggedness and permit the employment of the diaphragm as part of the external structure of the head phone. On the rear .ofthe housing I,

.is molded a pair ofridges 23, also "shown in the cross-sectional detail in Fig. '7, between'which ridges ispivoted'the flattened end of the head phone simportingsteni 25. A pin 24 isemployed to provide a hearing .for the end of the stem This pivot, plus the freedom of rotation of the wrod inthe mounting bracket 26, permits universal swivel motion of the head phone so thatiteasily sets itself to'tbe best orientation on a persons ear. A portion of the head band is shown attached. to the bracket 2d by means of A soft molded outer cover 29 of sealed chamber, considerable discomfort rresults from the high humidity that is created due to lack of adequate ventilation of the ear. The convex surface shown in Fig. 6 distributes the pressure very uniformly over various portions of the outer ear and head and also leaves ventilating slits between the folds of the ear structure and the convex surface when worn, which serve to keep the ear refreshed and comfortable. In the choice of the material for the cover 29, it is preferable to select one which attenuates sound to an increasing degree as the frequency is increased. The necessity for this choice of material results from the fact that the vibrating portion of the sound generator employing the construction described is stillness-controlled over a large portion of the audio-frequency range, which results in constant displacement of the diaphragm over a wide range of frequencies for constant generated driving force in the transducer element. If such a system is employed as a head phone and is not sealed to the car, as is the case in my new improved arrangement, the sound intensity generated will increase with increasing frequency. By employing material whose attenuation characteristic causes increased attenuation with increasing freouency, the proper balance between low and his frequency response may be maintained. Another method may be resorted to for proviclhig uniform response as a function of frequency in connection with the magnetic and magnetostriction systems indicated in Figs. 1, 2, 3, and 4:. It is possible to design the coil windings magnetic circuit such that the electrical. impedance of the unit is primarily an inductance over most of the frequency range. If such an impedance is connected across a circuit whose impedance is approximately equal to the resistive component of the coil impedance, the high-frequency compensation for the head phone may be electrically realized without resorting to accoustic attenuation in the cover ped 29. A combination of electrical and acoustic compensation is also possible for conditions where highest quality reproduction is essential. Although it is not shown, I may place holes through the center portion of the cover 29 for the purpose of reducing the high-frequency losses through the cover, if I so desire.

If any of the described transducers are used as microphones, the stiffness-controlled mechanical system will automatically result in uniform response versus frequency over the entire range of frequencies lying well below the resonant frequency of the diaphragm assembly. Any of the transducers, therefore, results in an ideal microphone for use under adverse conditions such as in a rain storm or at sea, where dependability and ruggedness are a primary concern in the installation.

Although I have shown several specific embodiments of my invention for the purposes of illustrating the novel features, there will be other variations that will be obvious to those skilled in the art. and I. therefore, desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination in electro mechanical transducer for generating sound waves in a gaseous medium, a housing having an opening, a vibratile diaphragm attached to said housing closing said opening, electro-mechanical force generating means attached to said housing and arranged to impart said generated forces to cause vibrations of said diaphragm only in directions substantially normal to the surface thereof, the mechanical compliance of the diaphragm lying in the approximate range 0.001 to 0.0003 inch displacement per pound of force applied at its center point.

2. The invention set forth in claim 1, characterized in that the active diameter of said diaphragm is not greater than 3 inches.

3. In a telephone receiver for generating sound waves in a gaseous medium, a body having an open side, electro-mechanical force generating means secured to said body, a diaphragm structure having a vibratile section secured to said body closing said open side, said force generating means being arranged to vibrate said diaphragm only in directions substantially normal to the surface thereof, the compliance of said vibratile section of said diaphragm structure being less than .001 inch displacement per pound force applied to its center, whereby said diaphragm protects said electro-mechanical generating means without aid of a grille or the like, and the resonance frequency of said diaphragm lying near the upper portion of the frequency range of operation of said telephone receiver.

4. The invention described in claim 3, characterized in that the vibratile section of saiddiaphragm structure is covered with a compressible material which offers greater attenuation to sound waves at the higher audio frequencies than at the lower audio frequencies.

5. In an electro-mechanical transducer for generating sound waves in a gaseous medium, a casing, a vibratile diaphragm supported by the casing, electro-mechanical force generating means disposed within the casing and arranged to impart vibrations to said diaphragm with respect to said casing and in directions substantially normal to the surface of said diaphragm substantially throughout the ordinary audio-frequency range of a radio program, said diaphragm having a mechanical compliance of less than 0.001 inch per pound of force applied at its center, and the resonance frequency of said diaphragm lying near the upper portion of the frequency range of operation of said transducer.

6. A vibratile diaphragm according to claim 5 further characterized in that the diaphragm is molded of plastic material and has a portion of said electro-mechanical force generating means anchored permanently therein.

'7. The invention set forth in claim 5, further characterized in that the shapes of said body por tion and said diaphragm portion are such as to present an external overall convex surface to the assembled transducer, a portion of said external surface serving as the vibrating element.

8. In an electro-mechanical transducer adapted to reproduce sound in gaseous media, a vibratile diaphragm, electro-mechanical force generating means arranged to impart vibrations to said diaphragm substantially throughout the ordinary audio-frequency range of a radio program and in directions substantially normal to the plane of said diaphragm, said diaphragm having a mechanical compliance of less than 0.001 inch per pound of force applied at its center point, and a cover disposed in contact with a vibratile portion of said diaphragm and composed of a compressible material which offers greater attenuation to sound waves at the higher audio-frequencies than at the lower audio-frequencies.

9. An electro-mechanical transducer adapted for the reproduction of intelligible speechin a gaseous medium, comprising a round, hollow sealed housing of generally ellipsoidal cross-section, said housing comprising a bod portion and a. vibratile diaphragm portion composed of mold ed plastic insulating material and presenting a smooth convex exterior surface, electro-mechanical force generating means within said housing and adapted to vibrate said diaphragm with respect to said housing in directions substantially normal to said diaphragm, said diaphragm having a mechanical compliance of less than 0.001 inch per pound of force applied to its center, whereby said diaphragm protects said force generating means without the aid of a grille or the like, said diaphragm having a plane marginal surface sealed to a plane marginal surface of the body portion, the inner surface of said diaphragm being undercut beneath the plane of said plane insulating material, said diaphragm having a plane marginal surface secured to a plane marginal surface of the body portion, an armature molded into the central portion of one of said portions and rigidly connected thereto and a field structure molded into the other of said portions and rigidly connected thereto, said armature and field structure having pole faces disposed in such relation to the planes of said plane marginal surfaces to provide an air gap when said diaphragm and body portions are assembled, said vibratile diaphragm portion having a mechanical compliance lying in the approximate range 0.001 to 0.0003 inch displacement per pound of force applied at its center point.

FRANK MASSA REFERENCES CITED The following references are of record in the file of this patent:

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